U.S. patent number 10,326,380 [Application Number 15/908,860] was granted by the patent office on 2019-06-18 for motor drive apparatus with function to detect abnormality in power device.
This patent grant is currently assigned to FANUC CORPORATION. The grantee listed for this patent is FANUC CORPORATION. Invention is credited to Shinichi Mizukami.
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United States Patent |
10,326,380 |
Mizukami |
June 18, 2019 |
Motor drive apparatus with function to detect abnormality in power
device
Abstract
A motor drive apparatus includes: a converter which converts AC
power to DC power and to output the DC power to a DC link; an
inverter including power devices which converts the DC power to AC
power for driving a motor; a capacitor provided in the DC link; a
shut-off circuit to open and close an electrical path between the
AC power source and the converter; a constant current control unit
which performs control in such a manner as to allow a constant
current supplied by the capacitor to pass through a detection
target power device among the power devices in the inverter; and an
abnormality detection unit which detects an abnormality in the
detection target power device based on changes in voltage between a
collector and an emitter of the detection target power device
during a period in which the constant current passes through the
detection target power device.
Inventors: |
Mizukami; Shinichi (Yamanashi,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
FANUC CORPORATION |
Yamanashi |
N/A |
JP |
|
|
Assignee: |
FANUC CORPORATION (Yamanashi,
JP)
|
Family
ID: |
63372551 |
Appl.
No.: |
15/908,860 |
Filed: |
March 1, 2018 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20180269804 A1 |
Sep 20, 2018 |
|
Foreign Application Priority Data
|
|
|
|
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Mar 14, 2017 [JP] |
|
|
2017-049022 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M
1/32 (20130101); H02M 7/4826 (20130101); H02P
27/00 (20130101); H02P 29/0241 (20160201); H02M
7/5387 (20130101); H02M 5/293 (20130101); H02P
3/00 (20130101); H02P 29/024 (20130101); H02P
2203/07 (20130101); H02P 2201/03 (20130101); H02M
2001/327 (20130101) |
Current International
Class: |
H02M
1/32 (20070101); H02P 29/024 (20160101); H02P
3/00 (20060101); H02M 7/48 (20070101); H02P
27/00 (20060101); H02M 5/293 (20060101); H02M
7/5387 (20070101) |
Field of
Search: |
;318/806 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
H6-115836 |
|
Apr 1994 |
|
JP |
|
H6-165480 |
|
Jun 1994 |
|
JP |
|
H7-170754 |
|
Jul 1995 |
|
JP |
|
H10-66388 |
|
Mar 1998 |
|
JP |
|
2002289856 |
|
Oct 2002 |
|
JP |
|
2012-229971 |
|
Nov 2012 |
|
JP |
|
Primary Examiner: Chan; Kawing
Attorney, Agent or Firm: Hauptman Ham, LLP
Claims
The invention claimed is:
1. A motor drive apparatus comprising: a converter configured to
convert AC power supplied by an AC power source to DC power and to
output the DC power to a DC link; an inverter including power
devices provided for an upper arm and a lower arm, which power
devices are ON/OFF controlled by respective gate voltages applied
thereto, to convert the DC power in the DC link to AC power for
driving a motor; a capacitor provided in the DC link; a shut-off
circuit configured to open and close an electrical path between the
AC power source and the converter; a constant current control unit
configured to perform control in such a manner as to allow a
constant current supplied by the capacitor charged with DC power to
pass through a detection target power device among the power
devices in the inverter; and an abnormality detection unit
configured to detect an abnormality in the detection target power
device based on changes in voltage between a collector and an
emitter of the detection target power device during a period in
which the constant current passes through the detection target
power device.
2. The motor drive apparatus according to claim 1, wherein the
constant current control unit comprises: a shut-off command unit
configured to issue a command to the shut-off circuit to shut off a
supply of AC power from the AC power source to the converter; a
current detection unit configured to detect a current passing from
the inverter to the motor; and a gate voltage adjustment unit
configured to adjust a gate voltage applied to a power device
provided for a different phase and a different arm from the phase
and the arm for which the detection target power device is
provided, based on the current detected by the current detection
unit, in such a manner as to allow the constant current supplied by
the capacitor charged with DC power to pass through the detection
target power device during a period in which the shut-off circuit
shuts off the supply of AC power from the AC power source to the
converter in accordance with the command by the shut-off command
unit.
3. The motor drive apparatus according to claim 2, wherein the gate
voltage adjustment unit regularly switches between one and another
of the power devices, gate voltages of which are adjusted by the
voltage adjustment unit, each of the power devices provided for a
different phase and a different arm from the phase and the arm for
which the detection target power device is provided.
4. The motor drive apparatus according to claim 1, wherein the
abnormality detection unit comprises: a voltage detection unit
configured to detect a voltage between the collector and the
emitter of each power device; a storage unit configured to store
changes in the voltage between the collector and the emitter of the
detection target power device detected by the voltage detection
unit during a first period in which the constant current passes
through the detection target power device; and a determination unit
configured to determine that an abnormality has occurred in the
detection target power device when a certain threshold value is
exceeded by an amount of difference between the changes in the
voltage between the collector and the emitter of the detection
target power device detected by the voltage detection unit and
stored in the storage unit and changes in voltage between the
collector and the emitter of the detection target power device
detected by the voltage detection unit in a second period in which
the constant current passes through the detection target power
device and which is previous to the first period.
5. The motor drive apparatus according to claim 1, wherein each of
the power devices is a semiconductor switching device that allows a
current of varying intensity to pass through the semiconductor
switching device as a function of the gate voltage applied.
Description
RELATED APPLICATIONS
The present application claims priority of Japanese Application
Number 2017-049022 filed Mar. 14, 2017, the disclosure of which is
hereby incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor drive apparatus with a
function to detect an abnormality in a power device.
2. Description of the Related Art
In motor drive apparatuses for driving motors in machine tools,
forming machinery, molding machines, industrial machinery, or
various robots, AC power supplied by an AC power source is
converted to DC power by a converter and then converted to AC power
by an inverter, and this AC power is used as drive power for motors
respectively provided for drive axes. The inverter includes a
bridge circuit constituting a switch unit having a power device
(semiconductor switching device) and a diode in antiparallel
connection thereto and converts DC power to AC power and outputs
the AC power by tuning on and off the power device.
When a current passes through a power device, the device heats up
and excessive heating would lead to an abnormality such as a
breakdown of the power device. To detect an abnormality in a power
device, it is preferable to use a temperature sensor, but it is
difficult to mount a temperature sensor directly on the
semiconductor chip of a power device.
As a technique known for detecting the temperature of a power
device without providing a separate temperature sensor, for
example, Japanese Unexamined Patent Publication (Kokai) No.
2002-289856 discloses an on-chip temperature detection device
including: a current-controlled semiconductor device including a
base terminal, a collector terminal, an emitter terminal, and a
diode based on p-n junction between the base terminal and the
emitter terminal; first means for allowing a certain base current
to pass through the base terminal when the control signal applied
to the base terminal is off, the certain base current being smaller
than a base current that would switch the current-controlled
semiconductor device to the normal ON state; second means for
detecting a temperature of the current-controlled semiconductor
device on the basis of a forward voltage between the base and the
emitter of the current-controlled semiconductor device when the
certain base current smaller than a base current that would switch
the current-controlled semiconductor device to the normal ON state
passes the base terminal, wherein the detection of the temperature
is conducted based on temperature dependence of the forward voltage
of the diode based on p-n junction in the OFF state of the
current-controlled semiconductor device.
SUMMARY OF INVENTION
An inverter is a component of a motor drive apparatus and includes
a plurality of power devices. Since a plurality of motor drive
apparatuses are provided in machine tools, forming machinery,
molding machines, industrial machinery, or various robots, a very
large number of power devices exist in these machines. However, to
provide a temperature sensor for each semiconductor chip in a large
number of power devices is disadvantageous because to do so will
increase the cost and size of the motor drive apparatuses. In
addition, it is difficult to mount a temperature sensor on the
semiconductor chip of a power device, and a temperature sensor
disposed in a place away from the semiconductor chip of the power
device (for example, on a case containing the power device) does
not measure the temperature of the power device accurately. Failure
to detect a heating of a power device of an inverter in a motor
drive apparatus may lead to less working efficiency or a serious
accident because the power device is not replaced in a timely
manner. A power device not yet destroyed by heat may be prematurely
replaced Thus, there is a demand for a cost-effective technique for
motor drive apparatuses for accurately detecting an abnormality in
a power device caused by heat.
According to one aspect of the present disclosure, provided is a
motor drive apparatus including a converter configured to convert
AC power supplied by an AC power source to DC power and to output
the DC power to a DC link; an inverter including power devices
provided for an upper arm and a lower arm, which power devices are
ON/OFF controlled by respective gate voltages applied thereto, to
convert the DC power in the DC link to AC power for driving a
motor; a capacitor provided in the DC link; a shut-off circuit to
open and close an electrical path between the AC power source and
the converter; a constant current control unit configured to
perform control in such a manner as to allow a constant current
supplied by the capacitor charged with DC power to pass through a
detection target power device among the power devices in the
inverter; and an abnormality detection unit configured to detect an
abnormality in the detection target power device based on changes
in voltage between a collector and an emitter of the detection
target power device during a period in which the constant current
passes through the detection target power device.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more clearly by referring
to the following accompanying drawings:
FIG. 1 illustrates a motor drive apparatus according to an
embodiment;
FIGS. 2A and 2B are circuit diagrams for illustrating operation
examples of the constant current control unit of the motor drive
apparatus according to an embodiment;
FIG. 3 illustrates relationships between the gate voltage, the
voltage between the collector and the emitter, and the collector
current of the power device;
FIG. 4 is a diagram for illustrating an operation of the voltage
detection unit in the abnormality detection unit of the motor drive
apparatus according to an embodiment;
FIG. 5 illustrates examples of the relationships between the
temperature of a detection target power device and the voltage
between the collector and the emitter when a constant current is
allowed to pass through the detection target power device;
FIG. 6A is a diagram for illustrating an abnormality detection
processing by the abnormality detection unit of the motor drive
apparatus according to an embodiment and illustrates an example of
a current passing through a detection target power device;
FIG. 6B is a diagram for illustrating an abnormality detection
processing by the abnormality detection unit of the motor drive
apparatus according to an embodiment and illustrates an example of
temperature inside the detection target power device;
FIG. 6C is a diagram for illustrating an abnormality detection
processing by the abnormality detection unit of the motor drive
apparatus according to an embodiment and illustrates an example of
voltage between the collector and the emitter of the detection
target power device; and
FIG. 7 is a flowchart illustrating an operation of the motor drive
apparatus according to an embodiment.
DETAILED DESCRIPTION
A motor drive apparatus with a function to detect an abnormality in
a power device will be described below with reference to the
drawings. In the drawings, like members are denoted by like
reference numerals. Constituent features denoted by like reference
numerals in different drawings are to be understood to have the
same functions. Further, the drawings are presented in various
scales to aid the readers' understanding.
FIG. 1 illustrates a motor drive apparatus according to an
embodiment. As an example, a case with a three-phase AC power
source 3 and a motor drive apparatus 1 to drive a three-phase AC
motor 2 will be described. Note that the present embodiment is not
limited to a particular number of phases and, for example, a
single-phase AC power source and a single-phase motor may be used.
In addition, the present embodiment is not limited to a particular
type of motor 2 and the motor 2 may, for example, be an induction
motor or a synchronous motor.
A motor control unit 17 to perform drive control on a motor 2 will
be described before a servo motor drive apparatus 1 according to an
embodiment is described. The motor drive apparatus 1, similarly to
common servo motor drive apparatuses, includes a motor control unit
17 and a velocity detection unit 18 and controls an inverter 12
configured to convert powers between the DC power of the DC link
and the AC power for driving the motor 2 or regenerative AC power.
The motor control unit 17 generates switching commands to control
the velocity, torque, or position of the rotor of the motor 2 based
on a velocity of (the rotor of) the motor 2 detected by the
velocity detection unit 18 (velocity feedback), a current passing
through the wiring of the motor 2 (current feedback), a certain
torque command, an operation program for the motor 2, etc. The
power conversion operation by the inverter 12 is controlled in
accordance with the switching commands generated by the motor
control unit 17.
As illustrated in FIG. 1, the motor drive apparatus 1 according to
an embodiment includes a converter 11, an inverter 12, a capacitor
13, a shut-off circuit 14, a constant current control unit 15, and
an abnormality detection unit 16.
The converter 11 converts the AC power supplied by the AC power
source 3 to DC power and outputs the DC power to the DC link. In
the example illustrated in FIG. 1, the converter 11 is constituted
as a three-phase rectifying circuit since the AC power source 3 is
a three-phase power supply. The converter 11 may be, for example, a
diode rectifying circuit, 120-degree conducting type rectifying
circuit, or a rectifying circuit based on a PWM switching control
method with a power device (semiconductor switching device)
inside.
A capacitor 13 is provided in a DC link connecting the DC output
side of the converter 11 and DC input side of the inverter 12. The
capacitor 13 is commonly called a DC link capacitor or a smoothing
capacitor and performs a function of storing DC power in the DC
link and reducing ripples of the DC output of the converter 11.
The inverter 12 has power devices on the upper arm and the lower
arm and, as the power devices are ON/OFF controlled by gate
voltages applied to them, converts the DC power of the DC link to
AC power to output the AC power for driving the motor 2. The
inverter 12 includes bridge circuits formed by power devices
respectively in antiparallel connection with diodes. The power
devices are ON/OFF controlled, for example, by gate voltages
produced based on a PWM switching control method. The inverter 12
is formed as a three-phase inverter in the example illustrated in
FIG. 1 as the motor 2 is a three-phase AC motor; it will be formed
as a single-phase inverter when the motor 2 is a single-phase AC
motor.
The power devices constituting the bridge circuits in the inverter
12 are semiconductor switching devices that allow a current of
varying intensity to pass through them as a function of the gate
voltage applied and may be, for example, unipolar transistors such
as FETs, bipolar transistors, IGBTs, thyristors, or GTOs. A
unipolar transistor such as an FET has a gate, a drain, and a
source as its terminals, a bipolar transistor has a base, an
emitter, and a collector as its terminals, and an IGBT has a gate,
an emitter, and a collector as its terminals, and a thyristor and a
GTO has a gate, an anode, and a cathode as their terminals. Note
that when bipolar transistors are used as the power devices that
allow a current of varying intensity to pass through them as a
function of the gate voltage applied, "gate voltage" is read as
"base voltage" in applying the aspect of the present disclosure.
Similarly, depending on the power devices used, "drain" and
"source" or "anode" and "cathode" are read as "emitter" and
"collector" in applying the aspect of the present disclosure.
In the normal operation mode for operating the motor 2, the
inverter 12 switches on and off the power devices inside in
accordance with switching commands received from the motor control
unit 17 and converts the DC power supplied by the converter 11
through the DC link into an AC power of desired voltage and desired
frequency to drive the motor 2 (inversion operation). The motor 2
thus operates by the supplied power of variable voltage and
variable frequency. Further, in the normal operation mode, when the
motor 2 slows down and regenerative power is generated, the
inverter 12 switches on and off the power devices inside in
accordance with switching commands received from the motor control
unit 17 and converts the regenerative AC power generated by the
motor 2 to DC power and returns the DC power to the DC link
(conversion operation). Further, in a mode for detecting an
abnormality of a power device (hereinafter referred to as "the
diagnosis mode"), which is different from the normal operation mode
and will be described later in detail, the inverter 12 is
controlled by the constant current control unit 15 in such a manner
as to allow a very small constant current to pass through the
detection target power device. Although FIG. 1 illustrates an
example in which the constant current control unit 15 performs
constant current control in the diagnosis mode through the motor
control unit 17, the constant current control unit 15 may directly
control the inverter 12.
The shut-off circuit 14 opens and closes the electrical path
between the AC power source 3 and the converter 11 in accordance
with commands received from the shut-off command unit 21, which
will be described later. The shut-off circuit 14 may be, for
example, an electromagnetic contactor or a relay. Similarly to
common motor drive apparatuses, in the normal operation mode for
operating the motor 2, the shut-off circuit 14 opens the electrical
path between the AC power source 3 and the converter 11 upon excess
current in the electrical path between the AC power source 3 and
the converter 11 in accordance with a command received from the
shut-off command unit 21 and shuts off the supply of AC power from
the AC power source 3 to the converter 11. The operation of the
shut-off circuit 14 in the diagnosis mode will be described
later.
To perform an abnormality detection processing on a detection
target power device, the operation is switched from the normal
operation mode to the diagnosis mode. The constant current control
unit 15 and the abnormality detection unit 16 mainly operate in the
diagnosis mode. The switchover from the operation mode to the
diagnosis mode is done by, for example, turning a key or pushing
down an operation button of the operation terminal of the numerical
control apparatus connected with the motor drive apparatus 1 or
pressing down an operation button provided for the motor drive
apparatus 1.
In the diagnosis mode, the constant current control unit 15 allows
a constant current to pass through a detection target power device
and the abnormality detection unit 16 determines whether or not an
abnormality has occurred in the detection target power devices. The
detection target power device is selected from among the power
devices existing in the inverter 12, and the constant current
control unit 15 and the abnormality detection unit 16 perform
processing on the selected detection target power device one at a
time. For example, detection target power devices are selected one
by one from among the power devices in the diagnosis mode and the
constant current control unit 15 and the abnormality detection unit
16 may perform processing on all the detection target power devices
one by one. In such a case, the process of selecting detection
target power devices from among the power devices and the series of
processing by the constant current control unit 15 and the
abnormality detection unit 16 are executed, for example,
automatically in accordance with a software program. Further, for
example, a detection target power device may be selected from among
the power devices by choice and the constant current control unit
15 and the abnormality detection unit 16 perform processing on the
selected device. In such a case, the instruction as to which one of
the power devices is selected as detection target power device can
be given by operating a certain key of the operation terminal of
the numerical control apparatus connected with the motor drive
apparatus 1 or pressing down an operation button provided for the
motor drive apparatus 1.
The constant current control unit 15 performs control to allow a
constant current to pass a detection target power device selected
among the power devices of the inverter 12, the constant current
being supplied by the capacitor 13 charged with DC power. As
described later in detail, in the diagnosis mode, the abnormality
detection unit 16 detects an abnormality in the detection target
power device, through which the constant current passes, based on
changes in the voltage between the collector and the emitter of the
detection target power device and the constant current control unit
15 serves to effectuate and control this constant current. The
constant current passing through the detection target power device
in the diagnosis mode may be much smaller than the current passing
through the power devices in the normal operation mode.
In particular, the constant current control unit 15 includes a
shut-off command unit 21, a current detection unit 22, and a gate
voltage adjustment unit 23.
The shut-off command unit 21 issues commands to the shut-off
circuit 14 to open or close the electrical path between the AC
power source 3 and the converter 11. In the diagnosis mode in which
to detect an abnormality in a power device, the shut-off command
unit 21 issues a command to the shut-off circuit 14 to open the
electrical path between the AC power source 3 and the converter 11
to shut off the supply of AC power from the AC power source 3 to
the converter 11. As described above, in the normal operation mode
for operating the motor 2, the shut-off command unit 21 issues a
command to the shut-off circuit 14 to open the electrical path
between the AC power source 3 and the converter 11 upon excess
current in the electrical path between the AC power source 3 and
the converter 11, similarly to common servo motor drive
apparatuses.
The current detection unit 22 detects the current passing from the
inverter 12 to the motor 2. A current detection unit, used for
detecting the current passing from the inverter 12 to the motor 2
for the control of the inverter 12 by the motor control unit 17,
may also serve as the current detection unit 22.
During the period in which the supply of AC power from the AC power
source 3 to the converter 11 is shut off by the shut-off circuit 14
in accordance with a command by the shut-off command unit 21 (i.e.,
in the diagnosis mode), the gate voltage adjustment unit 23 adjusts
the gate voltage applied to a power device provided for a different
phase and a different arm from the phase and the arm for which the
detection target power device is provided (hereinafter referred to
as "gate voltage adjustment target power device"), based on the
current detected by the current detection unit 22, to allow a
constant current supplied by the capacitor 13 charged with DC power
to pass through the detection target power device. Since a current
(i.e. a constant current supplied by the capacitor 13 charged with
DC power) preferably passes through the detection target power
device in the diagnosis mode, the gate voltage adjustment unit 23
applies to the detection target power device a gate voltage such as
to allow the passage of such a current.
The constant current control unit 15 includes a shut-off command
unit 21, a current detection unit 22, and a gate voltage adjustment
unit 23 and performs constant current control processing, details
of which will be described later.
The abnormality detection unit 16 detects an abnormality in the
detection target power device, based on changes in the voltage
between the collector and the emitter of the detection target power
device during the period in which the constant current passes
through the detection target power device (i.e., in the diagnosis
mode).
In particular, the abnormality detection unit 16 includes a voltage
detection unit 31, a storage unit 32, and a determination unit
33.
The voltage detection unit 31 detects the voltage between the
collector and the emitter of each power device. In particular, the
voltage, detected by the voltage detection unit 31, between the
collector and the emitter of the detection target power device
selected from among the power devices is stored in the storage unit
32 and used for determination processing by the determination unit
33.
The storage unit 32 stores the changes in the voltage between the
collector and the emitter of the detection target power device
detected by the voltage detection unit 31 during the period in
which the constant current passes through the detection target
power device (i.e., in the diagnosis mode). As described below,
since the voltage between the collector and the emitter of the
detection target power device is proportional to the temperature
inside the power device, the voltage between the collector and the
emitter of the detection target power device detected by the
voltage detection unit 31 in the diagnosis mode gradually decreases
as the temperature inside the power device gradually falls as time
passes. The storage unit 32 stores the changes in the voltage
between the collector and the emitter of the detection target power
device (i.e., changes in the trend of decrease in voltage) in order
of time. The storage unit 32 includes, for example, electrically
erasable and recordable non-volatile memory such as, for example,
EEPROM (registered trademark) or random access memory readable and
writable at high speed such as, for example, DRAM or SRAM.
Alternatively, the storage unit 32 may be provided in a region of a
storage device used for driving the motor 2 by the motor drive
apparatus 1 in the normal operation mode.
The determination unit 33 determines that an abnormality has
occurred in the detection target power device when a certain
threshold value is exceeded by the amount of difference between the
changes in the voltage between the collector and the emitter of the
detection target power device detected by the voltage detection
unit 31 and stored in the storage unit 32 and the changes in the
voltage between the collector and the emitter of the detection
target power device detected by the voltage detection unit 31
during a period in which a constant current passed through the
detection target power device and which is previous to the period
in which the voltage changes in question have been detected (i.e.,
during a diagnosis mode operation previous to the diagnosis mode
operation in which the voltage changes in question have been
detected). The "diagnosis mode operation previous to the diagnosis
mode operation in which the voltage changes in question have been
detected" is preferably a diagnosis mode operation executed when
the inverter 12 is in pristine condition (i.e., when the power
devices are also in pristine condition). In other words, while the
power devices are in pristine condition, the abnormality detection
unit 16 performs processing on each of the power devices of the
inverter 12 and the voltage between the collector and the emitter
of each power device detected by the voltage detection unit 31 is
stored in the storage unit 32 as default information. In subsequent
diagnosis mode operations, the abnormality determination unit 33
determines that an abnormality has occurred in the detection target
power device when a certain threshold value is exceeded by the
amount of difference obtained by comparing the changes in the
voltage between the collector and the emitter of the detection
target power device detected by the voltage detection unit 31 and
stored in the storage unit 32 with the changes in voltage between
the collector and the emitter of the detection target power device
stored as default information.
The result of determination by the determination unit 33 is
notified to the user of the motor drive apparatus 1. Examples of
means of notification to the user include a display device of a
personal computer, a mobile terminal, and a touch panel as well as
a display device mounted to the numerical control apparatus (not
illustrated) provided in the motor drive apparatus 1 and the result
of determination such as "an abnormality has occurred in the power
device" or "the power device is working normally" is expressed on
the display, for example, in letters and pictures. Further, for
example, notification may be made by means of audio equipment
producing voice or sounds such as a speaker, a buzzer, or chimes.
Further, notification may be made by printing the result of
determination on a sheet of paper by a printer. Further still,
these means may be combined as appropriate.
The constant current control processing by the constant current
control unit 15, which includes a shut-off command unit 21, a
current detection unit 22, and a gate voltage adjustment unit 23,
will be described next with reference to FIGS. 2A, 2B, and 3.
FIGS. 2A and 2B are circuit diagrams for illustrating operation
examples of the constant current control unit of the motor drive
apparatus according to an embodiment. In FIGS. 2A and 2B, the
constituent features of the motor drive apparatus 1 are omitted
except for the inverter 12 and the capacitor 13. FIG. 3 illustrates
relationships between the gate voltage, the voltage between the
collector and the emitter, and the collector current of the power
device;
The inverter 12 illustrated in FIGS. 2A and 2B is constituted as a
three-phase full-bridge inverter. The power device in R phase on
the upper arm is referred to SW.sub.RU, the power device in R phase
on the lower arm is referred to SW.sub.RL, the power device in S
phase on the upper arm is referred to SW.sub.SU, the power device
in S phase on the lower arm is referred to SW.sub.SL, the power
device in T phase on the upper arm is referred to SW.sub.TU, and
the power device in T phase on the lower arm is referred to
SW.sub.TL. Each power device is in antiparallel connection with a
diode. When, for example, the power device SW.sub.RU in R phase on
the upper arm is selected as the examination target power device
from among the power devices, constant current control processing
is performed as follows.
The power device, which is a semiconductor switching device that
allows a current of varying intensity to pass through it as a
function of the gate voltage applied, has voltage-current
characteristics as illustrated in FIG. 3. The numerical values in
FIG. 3 are given merely as an example and in practice each power
device has its own proper values. In addition, in FIG. 3, the gate
voltage V.sub.G is given in discrete values of 5 V, 10 V, 15 V, 20
V, and 25 V as an example but, needless to say, the values of the
gate voltage V.sub.G are not limited to these discrete values and
can take other values, for example, values between 5 V and 10 V. As
illustrated in FIG. 3, for example, with a gate voltage V.sub.G of
5 V applied to the power device, the collector current I.sub.C
increases as the voltage between the collector and the emitter
V.sub.CE increases as long as the voltage between the collector and
the emitter V.sub.CE is between 0 V and about 2 V; however, the
collector current I.sub.C reaches saturation and becomes a constant
current of about 25 A when the voltage between the collector and
the emitter V.sub.CE exceeds about 2 V. For example, with a gate
voltage V.sub.G of 10 V applied to the power device, the collector
current I.sub.C increases as the voltage between the collector and
the emitter V.sub.CE increases as long as the voltage between the
collector and the emitter V.sub.CE is between 0 V and about 4 V;
however, the collector current I.sub.C reaches saturation and
becomes a constant current of about 90 A when the voltage between
the collector and the emitter V.sub.CE exceeds about 4 V. Further,
for example, with a gate voltage V.sub.G of 15 V applied to the
power device, the collector current I.sub.C increases even when the
voltage between the collector and the emitter V.sub.CE is between 0
V and about 5 V. As described above, the power device has a
characteristic such that the collector current I.sub.C changes as a
function of the applied gate voltage V.sub.G and the voltage
between the collector and the emitter V.sub.CE. According to one
aspect of the present disclosure, the gate voltage adjustment unit
23 utilizes this characteristic of the power device to allow a
constant current to pass through the detection target power
device.
A constant current is effectuated as follows, using the capacitor
13 charged with DC power as supply source (generation source).
In the normal operation mode for operating the motor 2, the
inverter 12 converts the DC power supplied by the converter 11
through the DC link into an AC power of desired voltage and desired
frequency to drive the motor 2 and, at this time, the capacitor 13
provided in the DC link stores DC power. When the operation is
switched from the normal operation mode to the diagnosis mode, the
shut-off command unit 21 issues a command to the shut-off circuit
14 to open the electrical path between the AC power source 3 and
the converter 11 to shut off the supply of AC power from the AC
power source 3 to the converter 11. Thus, the capacitor 13 is
charged with DC power. The gate voltage adjustment unit 23 then
adjusts the gate voltage applied to a gate voltage adjustment
target power device provided for a different phase and a different
arm from the R phase and the upper arm, for which the detection
target power device is provided, to create a current path including
the gate voltage adjustment target power device, the detection
target power device, the motor 2, and the capacitor 13. The
capacitor 13 charged with DC power serves as the supply source for
a constant current passing through this current path.
FIG. 2A illustrates an example in which the power device SW.sub.TL
is selected as gate voltage adjustment target power device as the
power device SW.sub.TL is provided for T phase, which is a
different phase from R phase for which the detection target power
device SW.sub.RU is provided, and the power device SW.sub.TL is
provided for the lower arm, which is different from the upper arm
for which the detection target power device SW.sub.RU is provided.
Further, as illustrated in FIG. 2B, the power device SW.sub.SL may
also be selected as gate voltage adjustment target power device as
the power device SW.sub.SL is provided for S phase, which is a
different phase from R phase for which the detection target power
device SW.sub.RU is provided, and the power device SW.sub.SL is
provided in the lower arm, which is different from the upper arm in
which the detection target power device SW.sub.RU is provided. As
described above, for each detection target power device, there are
two potential gate voltage adjustment target power devices. At
least one of these two is selected as gate voltage adjustment
target power device.
The intensity of the constant current is controlled by the gate
voltage adjustment unit 23 as in the following process.
As illustrated in FIG. 2A, when the gate voltage adjustment unit 23
applies a gate voltage to the detection target power device
SW.sub.RU to allow a current to pass through it and adjusts the
gate voltage applied to the power device SW.sub.TL, a current path
is formed consisting of the capacitor 13, the detection target
power device SW.sub.RU, the R phase terminal of the motor 2, and
the T phase terminal of the motor 2, and the gate voltage
adjustment target power device SW.sub.TL, as depicted by thick
dotted line in the drawing. As a result, a current supplied by the
capacitor 13 charged with DC power as supply source (generation
source) passes through the detection target power device SW.sub.RU
and the gate voltage adjustment target power device SW.sub.TL. The
current passing through the detection target power device SW.sub.RU
and the gate voltage adjustment target power device SW.sub.TL is
detected by the current detection unit 22. The gate voltage
adjustment unit 23 adjusts the gate voltage in such a manner as to
keep the current detected by the current detection unit 22
constant.
A case will be described, as an example, in which a current path as
illustrated in FIG. 2A is formed in the diagnosis mode and the
voltage-current characteristics of the power device SW.sub.TL are
as illustrated in FIG. 3. When it is desired, for example, that a
constant current of 25 A should pass through the detection target
power device SW.sub.RU as its collector current I.sub.C and when
the voltage between the collector and the emitter V.sub.CE of the
detection target power device SW.sub.RU is 3 V, a gate voltage
V.sub.G of 5 V is applied to the gate voltage adjustment target
power device SW.sub.TL. However, since the supply of DC power from
the converter 11 is shut off by the shut-off circuit 14 in the
diagnosis mode, the capacitor 13 discharges as time passes, the DC
power (in other words, electric charge) stored in the capacitor 13
gradually decreases and the voltage across the capacitor 13
gradually decreases, which results in a gradual decrease in the
voltage between the collector and the emitter V.sub.CE of the
detection target power device SW.sub.RU. When, for example, the
voltage between the collector and the emitter of the detection
target power device SW.sub.RU decreases to 1.4 V and the gate
voltage V.sub.G applied to the gate voltage adjustment target power
device SW.sub.TL is kept at 5 V, the collector current I.sub.C of
the detection target power device SW.sub.RU will not be maintained
as a constant current of 25 A. To address this, the gate voltage
adjustment unit 23 makes adjustment by increasing the gate voltage
V.sub.G applied to the gate voltage adjustment target power device
SW.sub.TL to 10 V. The gate voltage adjustment unit 23 maintains
the gate voltage of the gate voltage adjustment target power device
SW.sub.TL as long as the collector current I.sub.C of the detection
target power device SW.sub.RU is in the saturation state, and the
gate voltage adjustment unit 23 makes adjustment by increasing the
gate voltage of the gate voltage adjustment target power device
SW.sub.TL when the collector current I.sub.C of the detection
target power device SW.sub.RU is out of the saturation state. The
above-described example refers to a case in which the gate voltage
of the power device SW.sub.TL is adjusted as in FIG. 2A, and the
adjustment is made in a similar manner when the gate voltage of the
power device SW.sub.SL is adjusted as in FIG. 2B. In other words,
regardless whether the gate voltage adjustment target power device
is SW.sub.TL or SW.sub.SL in relation to the detection target power
device SW.sub.RU, the gate voltage adjustment unit 23 performs the
same adjustment processing.
As described above, in the diagnosis mode, since the voltage
between the collector and the emitter V.sub.CE of the detection
target power device SW.sub.RU decreases as time passes due to a
decrease in the voltage across the capacitor 13, to maintain the
collector current I.sub.C passing through detection target power
device SW.sub.RU, the gate voltage adjustment unit 23 monitors the
current detected by the current detection unit 22 and makes
adjustment to keep this current constant by either "maintaining" or
"increasing" the gate voltage of the gate voltage adjustment target
power device SW.sub.TL. As described above, at least one of these
two power devices may be selected as gate voltage adjustment target
power device and, in a modified example, the gate voltage
adjustment unit 23, in selecting a gate voltage adjustment target
power device, may switch regularly between two power devices
provided for a different phase and a different arm from the phase
and the arm for which the detection target power device is
provided. This is advantageous in curtailing the heating of the
gate voltage adjustment target power devices during the diagnosis
mode.
With reference to FIGS. 4 to 6C, abnormality detection processing
by the abnormality detection unit 16, which includes the voltage
detection unit 31, the storage unit 32, and the determination unit
33, will now be described in detail.
FIG. 4 is a diagram for illustrating an operation of the voltage
detection unit in the abnormality detection unit of the motor drive
apparatus according to an embodiment. In the diagnosis mode, the
voltage detection unit 31 detects the voltage between the collector
and the emitter of the detection target power device through which
a constant current passes.
FIG. 5 illustrates examples of relationships between the
temperature of the detection target power device and the voltage
between the collector and the emitter when a constant current is
allowed to pass through the detection target power device. In the
diagnosis mode, the temperature of the detection target power
device through which a constant current passes falls as time
passes, which is accompanied by a decrease in the voltage between
the collector and the emitter of the detection target power
device.
In general, the temperature inside a power device and the voltage
between the collector and the emitter of the power device is in a
proportional relation with "K factor" as a proportionality
coefficient. The relation is expressed as in equation (1).
Temperature inside the Power Device [.degree. C.]=K Factor
[.degree. C./V].times.Voltage between the Collector and the Emitter
of the Power Device [V] (1)
Equation 1 is rearranged as equation 2. Voltage between the
Collector and the Emitter of the Power Device [V]=Temperature
inside the Power Device [.degree. C.]/K Factor [.degree. C./V]
(2)
From equation 2 it can be seen that the voltage between the
collector and the emitter of the power device is proportional to
the temperature inside the power device, the reciprocal of K factor
being the proportionality coefficient. In other words, as the
temperature inside the power device gradually falls as time passes,
the voltage between the collector and the emitter of the power
device also gradually decreases. It is reasonable to assume that
the trend of decrease in the voltage between the collector and the
emitter of the detection target power device during an operation in
the diagnosis mode is roughly the same as during an operation in
the diagnosis mode conducted at a different time if there is no
abnormality in the detection target power device (i.e., if the
device is not destroyed by heat). In contrast, when there is an
abnormality in the detection target power device, different trends
of decrease in the voltage between the collector and the emitter of
the detection target power device are observed between operations
in the diagnosis mode conducted at different times. Hence,
according to one aspect of the present disclosure, the abnormality
detection unit 16 observes changes in the voltage between the
collector and the emitter of the detection target power device
(changes in the trend of decrease in the voltage) when a constant
current passes through the detection target power device and
compares the observed voltage changes with voltage changes observed
in the past to detect an abnormality in the detection target power
device. Concrete examples are given below.
FIG. 6A is a diagram for illustrating abnormality detection
processing by the abnormality detection unit of the motor drive
apparatus according to an embodiment and illustrates an example of
a current passing through the detection target power device. FIG.
6B is a diagram for illustrating abnormality detection processing
by the abnormality detection unit of the motor drive apparatus
according to the embodiment and illustrates an example of
temperature inside the detection target power device. FIG. 6C is a
diagram for illustrating abnormality detection processing by the
abnormality detection unit of the motor drive apparatus according
to the embodiment and illustrates an example of voltage between the
collector and the emitter of the detection target power device.
FIGS. 6A, 6B, and 6C illustrates, as an example, an operation which
is in the normal operation mode from time 0 to t.sub.1 and in the
diagnosis mode from time t.sub.1 to time t.sub.2. In the normal
operation mode, the temperature of the power device (detection
target power device) rises as a current passes through it (FIG. 6B)
and the voltage between the collector and the emitter of the power
device (detection target power device) increases in proportion to
the temperature rise (FIG. 6C). When the operation is switched over
to the diagnosis mode at time t.sub.1, the constant current control
unit 15 performs control to shut off the supply of DC power from
the converter 11 and a constant current supplied by the capacitor
13 charged with DC power starts to pass through the detection
target power device. Since the constant current passing through the
detection target power device in the diagnosis mode is much smaller
than the current in the normal operation mode, the temperature
inside the detection target power device falls in the diagnosis
mode (FIG. 6B) and the voltage between the collector and the
emitter of the power device (detection target power device), which
is proportional to the temperature, also decreases in a trend
similar to the falling temperature (FIG. 6C). It is reasonable to
assume that the trend of decrease in the voltage between the
collector and the emitter of the detection target power device
during an operation in the diagnosis mode is roughly the same as
during an operation in the diagnosis mode conducted at a different
time if there is no abnormality in the detection target power
device. In contrast, when there is an abnormality in the detection
target power device, different trends of decrease in the voltage
between the collector and the emitter of the detection target power
device are observed between operations in the diagnosis mode
conducted at different times. FIG. 6B illustrates by broken line a
difference in temperature changes between operations in the
diagnosis mode conducted at different times, which results from an
abnormality in the detection target power device, and FIG. 6C
illustrates by broken line a difference in voltage changes between
operations in the diagnosis mode conducted at different times,
which results from an abnormality in the detection target power
device. In one aspect of the present disclosure, the abnormality
detection unit 16 detects an abnormality in the detection target
power device, based on the amount of this difference.
As described above, the abnormality detection unit 16 observes
changes in the voltage between the collector and the emitter of the
detection target power device (changes in the trend of decrease in
the voltage) in order of time when a constant current passes
through the detection target power device, and the abnormality
detection unit 16 stores this in the storage unit 32. The
determination unit 33 in the abnormality detection unit 16 compares
changes in the voltage between the collector and the emitter of the
detection target power device detected by the voltage detection
unit 31 in the diagnosis mode and stored in the storage unit 32
with the changes in the voltage between the collector and the
emitter of the detection target power device detected by the
voltage detection unit 31 during a period in which a constant
current passed through the detection target power device and which
is previous to the period in which the voltage changes in question
have been detected (i.e., during a diagnosis mode operation
previous to the diagnosis mode operation in which the voltage
changes in question have been detected) to calculate the amount of
difference. The determination unit 33 determines that an
abnormality has occurred in the detection target power device when
the calculated amount of difference exceeds a certain threshold
value.
The determination unit 33 can perform the abnormality determination
processing based on the amount of difference of the changes in the
voltage between the collector and the emitter of the detection
target power device by, for example, using the time integral of the
voltage between the collector and the emitter of the detection
target power device taken over the period of the diagnosis mode
operation. In other words, the abnormality determination processing
can be performed by calculating the time integral of the voltage
between the collector and the emitter of the detection target power
device detected by the voltage detection unit 31 in the diagnosis
mode and stored in the storage unit 32 and the time integral of the
voltage between the collector and the emitter of the detection
target power device detected by the voltage detection unit 31
during a diagnosis mode operation previous to the diagnosis mode
operation in question (preferably during a diagnosis mode operation
conducted when the detection target power device was new),
calculating the difference between these integral values, and
taking the absolute value of the calculated difference as the
amount of difference. When this amount of difference exceeds a
certain threshold value, the determination unit 33 determines that
an abnormality has occurred in the detection target power device.
Alternatively, the temperature time constant of the semiconductor
chip of the power device during the cooling period may be used as
the amount of difference.
The threshold value to be used for the determination processing by
the determination unit 33 can be appropriately established based on
the data accumulated by, for example, operating the motor drive
apparatus 1 either in experiment or in actual practical operation,
on the environment of use, frequency of destruction by heat, etc.,
for identical standard power devices. In this procedure, a
threshold value may be set at a value smaller than the absolute
value of the difference between the time integral of the voltage
between the collector and the emitter of the detection target power
device detected by the voltage detection unit 31 in an actual case
of a destruction by heat and the time integral of the voltage
between the collector and the emitter of the detection target power
device detected by the voltage detection unit 31 when the detection
target power device was in pristine condition. With determination
processing by the determination unit 33 based on this threshold
value, the user may be notified of an abnormality in the near
future before the power device is actually destroyed (i.e., before
an abnormality occurs). Experiences or desires of the user of the
motor drive apparatus 1 may additionally be taken into
consideration in setting the threshold value.
The motor drive apparatus 1 according to the above-described aspect
of the present disclosure enables accurate detection of an
abnormality in a power device caused by heat. It also allows cost
reduction as no temperature sensor is used. Further, based on the
result of detection by the abnormality detection unit 16, the user
of the motor drive apparatus 1 may be notified that "there is a
chance of an abnormality in the power device in the near future"
before an actual occurrence of abnormality in the power device. As
a result, it is possible to replace power devices before they fail,
not missing the appropriate timing for replacing power devices,
thereby preventing power device failures and serious accidents.
Since the power devices can be timely replaced, excessive allowance
in design can be reduced and the stock of power devices can be
decreased.
The above-described constant current control unit 15, the
abnormality detection unit 16, and the motor control unit 17 may be
realized, for example, by a software program or a combination of
electronic circuits of various kinds and a software program. When,
for example, these units are realized by a software program, the
above-described functions of these units are realized by a computer
that operates according to the software program or by an arithmetic
processing unit in a numerical control apparatus connected with the
motor drive apparatus 1 that executes the software program.
Alternatively, the constant current control unit 15, the
abnormality detection unit 16, and the motor control unit 17 may be
realized by a semiconductor integrated circuit with a software
program written therein to carry out the functions of these
units.
Further, for example, when a plurality of motor drive apparatuses 1
are employed and the control systems of the motor drive apparatuses
1 are connected with each other via a communication network,
results of determination by the abnormality detection units 16 of
the motor drive apparatuses 1 may be shared on a cloud server.
Further, for example, when a plurality of manufacturing cells each
including a machine tool equipped with a motor drive apparatus 1
are connected with each other via a communication network, results
of determination by the abnormality detection units 16 of the motor
drive apparatuses 1 may be shared by cell controllers superordinate
to the manufacturing cells or by a production control apparatus
superordinate to the cell controllers.
A manufacturing cell is a set of machine tools flexibly combined
for product manufacturing. A manufacturing cell is formed by, for
example, a plurality of machine tools or a plurality of kinds of
machine tools, and may be formed by any number of machine tools.
For example, a manufacturing cell may be a manufacturing line in
which a workpiece is machined by a plurality of machine tools and
made into a finished product. Further, for example, a manufacturing
cell may be a manufacturing line in which two or more articles
(components) respectively machined by two or more machine tools are
assembled by another machine tool in the manufacturing process into
a finished article (product). Further, for example, two or more
articles machined in two or more manufacturing cells may be
assembled into a finished article (product). Manufacturing cells
and cell controllers are communicably connected with each other via
a communication network such as an intranet. Manufacturing cells
are organized in a factory where the products are manufactured.
Cell controllers may be provided in the factory where manufacturing
cells are organized or in a building separate from the factory. For
example, cell controllers may be provided in a separate building
located on the same premise as the factory where manufacturing
cells are organized.
A production control apparatus is provided superordinate to cell
controllers. A production control apparatus is mutually
communicably connected with cell controllers and give instructions
to the cell controllers according to a production plan. A
production control apparatus may be provided in an office remotely
located from the factory. In such a case, the cell controllers and
the production control apparatus are mutually communicably
connected via a communication network such as the Internet.
In such a production system, a display device provided for a cell
controller or a production control apparatus may be caused to
display information such as identification information of a power
device in which it is determined that an abnormality has occurred,
identification information of the inverter including the power
device, identification information of the motor drive apparatus 1
including the inverter, and identification information of the
manufacturing cell including the motor drive apparatus 1. Instead
of or in addition to the display device, audio equipment may be
used to produce an alarm sound or a buzz to notify the user of an
abnormality detected in a power device. This allows the workers and
supervisors working in the factory to learn easily that there is a
chance of an abnormality in the power device in the near future
before the power device is actually destroyed by heat (i.e., before
an abnormality occurs). As a result, it is possible to replace
power devices before they fail, not missing the appropriate timing
for replacing power devices, thereby preventing power device
failures and serious accidents.
FIG. 7 is a flowchart illustrating an operation of the motor drive
apparatus according to an embodiment.
In Step S101 the abnormality detection unit 16 performs processing
on each of the power devices in the inverter 12 when they are in
pristine condition and, for each of the power devices, the changes
in the voltage between the collector and the emitter detected by
the voltage detection unit 31 are stored in the storage unit 32 as
default information.
In S102, the motor drive apparatus 1 stops the normal drive
operation of the motor 2 and switches from the operation mode over
to the diagnosis mode. From Step S102 onwards, the motor drive
apparatus 1 operates in the diagnosis mode. The switchover from the
operation mode to the diagnosis mode is done by, for example,
operating a certain key of the operation terminal of the numerical
control apparatus connected with the motor drive apparatus 1 or
pressing down an operation button provided for the motor drive
apparatus 1.
In Step S103, the shut-off command unit 21 issues a command to the
shut-off circuit 14 to open the electrical path between the AC
power source 3 and the converter 11. The supply of AC power from
the AC power source 3 to the converter 11 is thereby shut off.
In Step S104, the gate voltage adjustment unit 23 applies a gate
voltage to the detection target power device to allow a current
pass through the detection target power device. This turns on the
detection target power device.
In Step S105, the gate voltage adjustment unit 23 adjusts the gate
voltage applied to a gate voltage adjustment target power device
which is provided for a different phase and a different arm from
the phase and the arm for which the detection target power device
is provided, based on the current detected by the current detection
unit 22. This allows a constant current supplied by the capacitor
13 charged with DC power to pass through the detection target power
device.
In Step S106, the voltage detection unit 31 detects the voltage
between the collector and the emitter of the detection target power
device. The values detected are sent to the storage unit 32.
In Step S107, the storage unit 32 stores the changes in the voltage
between the collector and the emitter of the detection target power
device detected by the voltage detection unit 31.
In Step S108, the determination unit 33 compares the changes in the
voltage between the collector and the emitter of the detection
target power device detected by the voltage detection unit 31 and
stored in the storage unit 32 with the changes in the voltage
between the collector and the emitter of the detection target power
device stored as default information and determines whether or not
the amount of difference obtained by the comparison exceeds the
threshold value.
When it is determined in Step S108 that the amount of difference
exceeds the threshold value, the determination unit 33 determines
that an abnormality has occurred in the detection target power
device (Step S109).
When it is not determined in Step S108 that the amount of
difference exceeds the threshold value, the determination unit 33
determines that the detection target power device is in a normal
condition (Step S110).
The result of determination in Step S109 and Step S110 is notified
to the user of the motor drive apparatus 1.
According to one aspect of the present disclosure, a motor drive
apparatus that allows accurate detection of an abnormality in a
power device caused by heat can be achieved at a low cost. Further,
the user of the motor drive apparatus is notified that there is a
chance of an abnormality in a power device in the near future
before an actual occurrence of abnormality. As a result, it is
possible to replace power devices before they fail, not missing the
appropriate timing for replacing power devices, thereby preventing
power device failures and serious accidents. Since the power
devices can be timely replaced, excessive allowance in design can
be reduced and the stock of power devices can be decreased.
* * * * *